Concentration Of Nitrogen Atoms Research Articles

On the Effects of the Thermal Treatment on the Structural, Mechanical and Tribological Properties of Amorphous Carbon-Nitrogen Films Deposited by Magnetron Sputtering

ABSTRACTAmorphous carbon-nitrogen films, a-CNx, deposited by rf-magnetron sputtering in N2 atmosphere were annealed in vacuum at temperatures between 300 and 700 °C. The annealing time was 30 minutes. The modifications on the film microstructure were monitored by infrared spectroscopy (IR), while the composition and the atomic density were determined by Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA). The internal stress was determined by measuring the film-induced bending of the substrate and the hardness was measured by nanoindentation. Atomic force microscopy (AFM) provided the friction coefficient and the surface roughness. The ratio between nitrogen and carbon atomic concentration decreases for temperatures higher than 500 °C, whereas the film density increases with the annealing temperature: 40 % in the temperature range here studied. The behavior of the D and G Raman bands, IR active due to the nitrogen incorporation in the carbon network, suggests a progressive increase of the size of the graphite-like domains. The hardness of the as-deposited a-CNx film is around 2 GPa. However, both hardness and internal stress increase by a factor of three in samples annealed at 700 °C, while the surface roughness and the friction coefficient decrease by a factor of about two.

Low energy, high current density ion implantation of materials at elevated temperatures for tribological applications

Low energy, high current density ion implantation at elevated temperatures has been shown to improve significantly the tribological properties of various materials. This paper summarizes the results published previously in this research area and presents some new results. Comparisons of this technique are made with ion nitriding and high energy ion implantation conducted under similar conditions (treatment temperature, treatment time and so on) on austenitic stainless steel and tool steel materials. The microstructural analyses and tribological evaluations presented here show that all three techniques generate almost identical microstructures on each metal studied, but low energy ion implantation produces treated layers with higher nitrogen concentrations and deeper diffusion, leading to higher wear resistance. A physical model is proposed to explore the mechanisms for these advantageous phenomena. The analysis suggests that a high current density is the primary mechanism responsible for the formation of deep nitrogen-containing layers. The ion energy is of secondary importance, as long as it is sufficiently high to overcome certain surface barrier potentials, to allow the removal of native oxide layers, to prevent surface oxidation and to allow the build-up of a high concentration of atomic nitrogen on the top of the treated surface to facilitate subsequent fast diffusion. Some applications and limitations of this technique are also addressed. It seems evident that low energy implantation (slightly higher than for ion nitriding, but much lower than for high energy ion implantation) at high current densities (much higher than those used in both ion nitriding and high energy implantation) generates superior nitrogen-containing layers on many materials, and hence the superior tribological performance compared to the other two techniques.

Effect of Nitrogen Profile on Tunnel Oxynitride Degradation with Charge Injection Polarity

The relationship between nitrogen profiles and polarity dependence of wearout and breakdown in oxynitride films was investigated. With positive bias stress, higher concentration of nitrogen atoms near an oxynitride/Si interface (∼2 at.%) and in the oxynitride bulk (∼0.3 at.%) reduce charge trap and interface state generation, and produce greater charge-to-breakdown (Q bd). In contrast, with negative bias stress, nitrogen atoms near an interface decrease the number of charge traps, but, cannot reduce interface state generation, and thus give smaller Q bd. Furthermore, nitrogen atoms near an oxynitride surface (over 1.5 at.%) cause undesirable results for both bias stresses. Optimum nitrogen profile in an oxynitride film is discussed the viewpoint of reliability for both bias stresses.

Bonding Defects in Hydrogenated Amorphous Silicon

AbstractA mechanism for charged-carrier-trapping-inducedde fect metastability in hydrogenated amorphous silicon (a-Si:H) and in hydrogenated amorphous silicon alloys containing relatively high concentrations of oxygen and/or nitrogen atoms (a-Si:X:H, X = O or N) is described. The experimental results that identified this defect metastability mechanism were i) differences in the Staebler-Wronski effect in a-Si:H and a-Si:N:H alloys prepared from N2 and NH3 source gases by remote plasma-enhanced chemical-vapor deposition, and ii) differences in defect generation at N-atom terminated Si-SiO2 interfaces prepared from NH3 and N2O.

Chemical deposition of Bi 2S 3 thin films on glass substrates pretreated with organosilanes

The chemical deposition of Bi 2S 3 thin films on glass substrates modified by treatment with solutions of 3-mercaptopropyltrimethoxysilane and 3-aminopropyltrimethoxysilane is described. Such treatment helps prevent the peeling of thin films, a problem which is otherwise encountered in the chemical deposition process. Uniform thin films having thicknesses up to 0.32 μm were obtained on the modified surfaces. X-ray photoelectron spectroscopy was employed to demonstrate that silanization takes place at the surfaces of the glass substrates. The relative atomic concentrations of nitrogen or sulfur on these surfaces increase with the time of immersion in the silanizing solutions. X-ray diffraction patterns of air-annealed Bi 2S 3 thin films were obtained. Optical transmittance and photoconductivity were measured and compared with those of the thin films deposited on untreated glass substrates. It was found that the thin films deposited on the silanized substrates were stable at 200 °C and maintain their original physical characteristics.

XPS film thickness and adsorption studies of alkyltrimethylammonium bromides and organosilanes on silica surfaces

The film thickness of organic molecules adsorbed onto a substrate may be predicted by a simple comparison of relative atomic concentrations if a well characterised film is used to form a calibration curve. Values of the attenuation length determined by X-ray photoelectron spectroscopy (XPS) are therefore not required. Cetyltrimethylammonium bromide (CTAB) is ideal as a calibration standard, because the formation of a surface layer below the critical micelle concentration (CMC) is found to be readily monitored by a comparison of the relative atomic concentrations of nitrogen and bromide. Ex-situ XPS results show direct evidence of the presence of surface nitrogen and absence of surface bromide when silica plates are removed from CTAB solutions at concentrations below the CMC. Results suggest that the structure of surface layers of CTAB determined ex-situ are not representative of the reported structure and orientation in-situ. At concentrations above the CMC, both nitrogen and bromide are found to be present on the surface. Angle resolved XPS of CTAB films formed above the CMC show that bromide ions do not simply occupy the outermost surface layer, which would be expected for a bilayer, rather a film of unknown structure is formed which is different from the surface of pure solid CTAB. For octyltrimethylammonium bromide and dodecyltrimethylammonium bromide, adsorption is limited to a narrow range of concentrations below their CMC values. The film thicknesses of the CTAB layers are compared with those previously reported for films of long chain alcohols adsorbed onto silica.

Nitridation of GaAs surfaces using nitrogen through a hot tungsten filament

This letter reports the nitridation of GaAs surfaces using N2 through a hot tungsten filament. After nitridation, GaAs cap layers were grown by molecular beam epitaxy to form GaAs/GaN/GaAs structures. For these structures, we determine the sheet nitrogen atom concentration by secondary ion mass spectrometry analysis. The sheet nitrogen atom concentration is proportional to the square root of the N2 pressure, indicating that N2 molecules are decomposed into nitrogen atoms to adsorb on the GaAs surfaces. The activation energy of this decomposition process is 3.6±0.4 eV.

Reliability of nitrided Si–SiO2 interfaces formed by a new, low-temperature, remote-plasma process

Controlled amounts of nitrogen atoms have been incorporated at Si–SiO2 interfaces by a new, low-temperature (300 °C), remote-plasma process, and corresponding improvements in device reliability are reported. Interfacial nitrogen-atom concentrations, up to 1×1015 cm−2, were obtained by a predeposition, remote plasma-assisted oxidation using mixtures of N2O and O2. Auger electron spectroscopy and secondary ion mass spectrometry studies to analyze N-atom concentrations at Si–SiO2 interfaces are discussed. Also, the results of electrical testing of submicron, n-channel metal–oxide–silicon field-effect transistors fabricated with this new process technology are reported. We found that the incorporation of N atoms at the Si–SiO2 interface increased current drive capability at high gate voltages but did not affect the threshold voltage of devices or the peak channel transconductance, gm. Device reliability, as measured by resistance to peak gm degradation after hot-carrier stressing, was found to increase with increasing N-atom concentrations at the Si–SiO2 interface.

Plasma-enhanced growth, composition, and refractive index of silicon oxy-nitride films

Secondary ion mass spectrometry and refractive index measurements have been carried out on silicon oxy-nitride produced by plasma-enhanced chemical vapor deposition (PECVD). Nitrous oxide and ammonia were added to a constant flow of 2% silane in nitrogen, to produce oxy-nitride films with atomic nitrogen concentrations between 2 and 10 at. %. A simple atomic valence model is found to describe both the measured atomic concentrations and published material compositions for silicon oxy-nitride produced by PECVD. A relation between the Si–N bond concentration and the refractive index is found. This relation suggest that the refractive index of oxy-nitride with a low nitrogen concentration is determined by the material density. It is suggested that the relative oxygen concentration in the gas flow is the major deposition characterization parameter, and that water vapor is the predominant reaction by-product. A model, that combine the chemical net reaction and the stoichiometric rules, is found to agree with measured deposition rates for given material compositions. Effects of annealing in a nitrogen atmosphere has been investigated for the 400 °C– 1100 °C temperature range. It is observed that PECVD oxy-nitrides release nitrogen and hydrogen in the form of NH for annealing temperatures in the 500 °C–700 °C range. The relaxation process during annealing is found to be governed by a viscoelastic relaxation process similar to the relaxation process observed for thermally grown SiO2. Upon nitrogen release, the PECVD material is in a state of internal tension. The viscoelastic relaxation process for temperatures above 700 °C is dominated by the relaxation of this internal tension. A linear relation between the refractive index and material density is determined for silicon oxy-nitride with a nitrogen concentration below 30 at. %.

Effects of ECR N2O-Plasma Nitridation on Thermal Oxide Characteristics

AbstractThe effects of electron cyclotron resonance (ECR) N2O-plasma nitridation on the characteristics of thermal SiO2 have been investigated. Although the ECR N2O-plasma nitridation was performed at low-temperature(≤400°C), it was found that oxynitride layer can be successfully grown at the Si/SiO2 interface. The atomic concentration of nitrogen near the Si/SiO2 interface was comparable to that of high temperature N2O annealing. The ECR N2O-plasma nitrided thermal SiO2 exhibits higher breakdown field characteristics, higher time-to-breakdown and charge-to-breakdown values in comparison with those of thermal SiO2. In addition, ECR N2O-plasma nitrided thermal SiO2 shows improved charge trapping properties

Ion-beam-assisted deposition of molybdenum nitride films

A series of molybdenum nitride films was synthesized by electron beam evaporative deposition of molybdenum, with simultaneous bombardment by nitrogen ions from a Kaufman ion source. The nitrogen ions were accelerated to 500 or 1000 eV. The film compositions and structures were determined using Rutherford backscattering spectrometry and X-ray diffraction respectively. Effective reflection and sputtering coefficients for nitrogen incident on the molybdenum nitride surfaces were extracted from the data. These coefficients were used to calibrate the deposition system and allowed the deposition of molybdenum nitride films with control of the nitrogen atom concentration to ±2.3 at.%. In general, the films were polycrystalline with a high degree of texturing. The phases found in order of increasing measured nitrogen content were as follows: γ-Mo2N (f.c.c.), β-Mo16N7 (b.c.t.), B1-MoN (f.c.c.) then δ-MoN (h.c.p.).

Photo-assisted metalorganic vapor-phase epitaxy for nitrogen doping and fabrication of blue-green light emitting devices of ZnSe-based semiconductors

Photo-assisted metalorganic vapor-phase epitaxy was proposed as a promising technique for acceptor doping in ZnSe-based semiconductors. The growth was carried out using diethyzinc and dimethylselenide as source precursors, and tertiarybutylamine as a dopant material. Photoluminescence, electrical properties of Schottky diodes, and electroluminescence of junction diodes supported p-type behavior of the ZnSe:N layers. As an example, net acceptor concentration was estimated as 2 × 10 17 cm -3 for the ZnSe:N layer with nitrogen atomic concentration of 5 × 10 17 cm -3. However, it was also pointed out that the doping characteristics were seriously affected by purity of source precursors, and this problem should be overcome, together with optimization of doping conditions, in order to achieve higher acceptor concentrations without heavy compensation.

Gas source molecular beam epitaxy of ZnSe and ZnSe:N

The use of gas source molecular beam epitaxy, using hydrogen selenide and elemental Zn as source materials, has resulted in the growth of high quality ZnSe on closely lattice-matched GaAs and (In,Ga)P. The undoped ZnSe epilayers are comparable in quality to material grown by molecular beam epitaxy, as indicated by narrow double-crystal x-ray diffraction rocking curves and intense photoluminescence dominated by a single donor-bound near-bandedge excitonic feature. Nitrogen species, derived from a radio frequency plasma source, are successfully used as acceptor impurities for ZnSe; photoluminescence spectra confirm the incorporation of nitrogen by the presence of the expected donor-to-acceptor pair recombination. Atomic concentrations of nitrogen as high as 5 x 1018 cm-3, are measured by secondary ion mass spectroscopy. Thus far, capacitance-voltage measurements indicate net acceptor concentrations (NA -ND) of approximately 1017 cm-3.

Surface Characterization and Platelet Adhesion Studies of Plasma-Carboxylated Polyethylene

Carboxyl groups were incorporated onto low-density polyethylene (LDPE) by carbon dioxide (CO 2) plasma modification, ammonia (NH 3) plasma modification with subsequent β-propiolactone (C 3H 4O 2) chemical grafting, and allylamine (CH 2=CHCH 2NH 2) plasma polymerization with subsequent β-propiolactone chemical grafting. ESCA and contact-angle experiments indicated that the hydrophilicity of the carbon dioxide plasma treated LDPE decreased with time due to the diffusion of the hydrophilic oxygen-containing functional groups away from the surface regions and/or the loss of the low molecular weight polar fragments. In contrast, the surface hydrophilicity of the β-propiolactone carboxylated ammonia and allylamine plasma treated LDPE determined by contact angle experiments was stable with time, but ESCA experiments showed that surface oxygen atomic concentration increased with time because of extensive post-plasma-treatment oxidation in air. The surface nitrogen atomic concentrations of both kinds of β-propiolactone carboxylated materials decreased with time due to diffusion of the nitrogen-containing functional groups into the bulk of the materials and/or the loss of the low molecular weight fragments to the environment. The blood compatibility of the carboxylated materials was examined by in vitro canine platelet adhesion as assessed by SEM. All three types of the plasma modified materials were more platelet reactive than the control LDPE base which suggests these materials are thrombogenic.

On the doping efficiency of nitrogen in hydrogenated amorphous germanium

This letter reports on the doping efficiency of nitrogen in a-Ge:H films of electronic quality. It has been found that nitrogen is an effective dopant in the a-Ge:H network, its doping efficiency being similar to the one corresponding to phosphorus in a-Si:H. The concentration of active nitrogen atoms decreases with impurity content following a square root dependence on total nitrogen. This behavior is similar to the one determined for column V dopants in a-Si:H films of electronic quality.

On the dilatation of synthetic type Ib diamond by substitutional nitrogen impurity

Sequences of high Bragg-angle (0 B = 74°) double-crystal X-ray topographs taken at the SRS (Daresbury, U.K.) have yielded precise measurements of lattice parameter differences between growth sectors of different crystallographic forms in a large undoped synthetic diamond whose type Ib infrared absorption spectrum (principal peak at 1130 cm -1 ) indicated atomically dispersed nitrogen, singly substituting for carbon, as the only detectable impurity. The plate-shaped specimen, polished parallel to (110), 5.0 x 3.2 mm 2 in area, 0.7 mm thick, possessed an unusually well developed (110) growth sector containing nitrogen impurity concentration of only ca. 10 -6 , which served as an internal standard of pure-diamond lattice parameter with which lattice parameters of nitrogen-containing growth sectors were compared. The specimen’s suitability for precision diffractometry was checked by comprehensive tests using optical microscope techniques, cathodoluminescence and single-crystal X-ray topography. The double-crystal combination was silicon reference crystal, asymmetric 175 reflection, with diamond specimen symmetrical 440 reflection. The principal measurement was the increase of the lattice parameter, a 0 , of the (111) growth sector (nitrogen content 88 + 7 parts per 10 6 atomic) relative to that of the (110) sector: Aa 0 / a 0 = 1.18 + 0.07 x 10 -5 . In terms of measured infrared absorption coefficient at 1130 cm -1 , this gives Aa 0/a 0 = (2.95 + 0.27) x 10 -6 [p(1130 cm -1 )/cm -1 ], which is believed to hold for growth sectors of all crystallographic forms. Combination with the nitrogen assay findings of Woods, van Wyk & Collins ( Phil. Mag. B 62. 589-595 (1990)) provides a direct relation to c N , the fractional atomic concentration of substitutional nitrogen, as A a 0 / a 0 = (0.14 + 0.02) c N , which indicates that the effective volume of a single substitutional nitrogen atom in diamond is 1.41 +0.06 times that of the carbon atom it replaces. This substantial dilatation conflicts with several models for the substitutional nitrogen structure.

Effect of process parameters on the atomic nitrogen concentration as measured by chemiluminescence in a post-discharge nitriding reactor

In the present work, the nitriding process has been performed in microwave (2450 MHz) post-discharges. The operating conditions for the ArN 2 and ArN 2H 2 post-discharges were a gas pressure in the range 3–100 hPa, a transferred h.f. power of 70–80 W and a flow rate of between 300 and 2000 N cm 3 min −1, giving a high gas velocity. The steel substrates were externally heated to reach the nitriding temperature. Quantitative results on atomic nitrogen concentration downstream from the microwave discharge have been obtained by NO chemiluminescence. This concentration has been studied as a function of the main process parameters. Correlation has been found between the atomic nitrogen concentration and the chemical composition and depth of the iron nitride layers growing on steel surfaces which are located in the post-discharge.

Nitrogen microwave discharge as a source of excited neutral species for possible surface treatment

A 2450 MHz surface-wave microwave flowing discharge, in pure N 2 or in ArN 2 mixtures, was used in order to understand the kinetics of the transport of atomic nitrogen along the postdischarge. Atomic nitrogen concentrations were measured by means of a chemiluminescent method of NO titration along the afterglow and some simple kinetic models are presented. These models take into account homogeneous and heterogeneous recombination and, if necessary, reactions between atomic nitrogen and some excited species of N 2.

Nitrogen atom recombination in high pressure Ar-N2 flowing post-discharges

The afterglow resulting from the nitrogen atom recombination in a flowing Ar-N2 microwave discharge (915 MHz and 100 W) is characterized by the first positive emission from N2 (B,V'). This emission occurs with a vibrational enhancement which is shifted from V'=11 in pure nitrogen to V'=8 in an Ar-2%N2 mixture. The N-N recombination rates producing N2(B,V') in Ar-x%N2 mixtures (x varies from 2-100%) were calculated from the measurement of the first positive emission intensity by spectrometry and the determination of the nitrogen atom concentration by a NO titration. Normalized values were obtained from previous published data in pure nitrogen.

The nitrogen content of type Ib synthetic diamond

Abstract The concentration of single nitrogen atoms in type Ib synthetic diamond has been measured, by electron paramagnetic resonance and by inert-gas fusion, as a function of the strength of the infrared absorption produced by these centres. The two methods yield, in good agreement, values of 22·0 ±.1·1 at. p.p.m. and 20·6±1·5 at. p.p.m. respectively, for an absorption coefficient of 1cm −1 at 1130 wavenumbers. These values agree tolerably well with an earlier value of 25 at. p.p.m./cm−1 given by others, so calling into question the generally accepted data pertaining to the strength of the infrared absorption produced by the A centres, or nitrogen pairs, found in type Ia (natural) diamond.